Compared with spherical and quadric surfaces, aspheric surfaces have more degrees of design freedom. If aspheric surfaces are used in off-axis three-mirror optical systems, the aberrations of the off-axis three-mirror optical systems can be significantly reduced, while the freedom of the off-axis three-mirror optical systems can be greatly improved.
However, conventional off-axis aspheric three-mirror optical system are mainly applied to linear field of view with small field angles and large F-number, but the applications in the field of view with large field angles and small F-number are limited.